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What is Bitmapped indexes? What is b-tree index in oracle?In a Bitmap index, a 2 dimensional array is created. The array represents the index value multiplied by number of rows. One column is allotted for every row in the table being indexed. When a row is retrieved, the bitmap is decompressed into the RAM data buffer to rapidly scan for matching values. Each matching value is returned as a ROW ID which can be used to access the desired information.
B-tree indexes are usually created on columns containing the most unique values. It is an ordered set of entries in which each entry a search key value and and a pointer to a specific row with that value. When a server finds a search key value matching a constraint, the pointer is used to fetch the row.
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